Hello Hauke,
I am not sure which version you are using
Changing the prompt screen is a common question; I don't know of a way you can change it. Having attended several conferences, speakers have said it is a dashboard best practice not to have prompts on dashboards.
I don't recall seeing it in the roadmap - you can check the most recent one at service.sap.com/roadmap
You can enter an idea at Idea Place at ideas.sap.com
Right now Design Studio does not have variant support either
You could design your dashboard at a summary level and then allow filters or check out the 1.6 "ready to run" templates to see if they can help